1. Field of the Invention
This invention relates to an X-ray imaging system for diagnostic use, and in particular to an X-ray radiography system including X-ray image intensifier tube and a video camera, for pickup of the output image of the image intensifier tube.
2. Description of the Prior Art
The combination of an X-ray image intensifier tube and a video camera is employed in various diagnostic systems such as for example, X-ray television systems and X-ray radiography systems. In a digital radiography (DR) system, video signals, obtained by use of an X-ray image intensifier tube and a video camera, are converted into digital data, which is provided to an image processor. According to the Digital Fluoroscopic Angiography (DFA) technique disclosed in U.S. Pat. No. 4,204,225, contrast images of vessels are produced by subtracting post-injection image data from pre-injection image data.
Many commercial digital radiography systems employ X-ray image intensifier tubes having an image input diameter varying between 229 to 406 mm. The output image diameter of these tubes is from 20 to 35 mm. The ratio of the input image to the output image (inverse number of image reduction ratio) exceeds 9.
X-ray image intensifier tubes for performing direct fluoroscopic observation are known. The output image diameter of this type of tube is 100 mm and the ratio of the input image diameter and the output image diameter is 5.7. Another tube of this type has output image diameter of 205 mm with the same input diameter as the 100 mm tube.